Process for preparing acetylene by the Sachsse-Bartholomé process

Abstract

A process is proposed for preparing acetylene by the Sachsse-Bartholomé process by combustion of a natural gas/oxygen mixture in one or more burners to obtain a cracking gas which is cooled in two or more stages in burner columns, each burner having one or more burner columns assigned thereto, and said cracking gas being quenched with pyrolysis oil in the first cooling stage, to obtain a low boiler fraction comprising benzene, toluene and xylene from the one or more burner columns, which is cooled with direct cooling water and separated in a phase separator into an aqueous phase and an organic phase which comprises benzene, toluene and xylene and is fully or partly introduced to the top of the one or more burner columns as a return stream, wherein the organic phase comprising benzene, toluene and xylene from the phase separator, prior to full or partial recycling to the top of the one or more burner columns, is supplied to a selective hydrogenation over a catalyst which comprises at least one platinum group metal on an inorganic metal oxide as support, comprising 0.05 to 5% by weight of platinum group metal, based on the total weight of the catalyst, and wherein the selective hydrogenation is performed at a pressure in the range from 10 to 70 bar gauge and a temperature in the range from 0 to 100° C.

The invention claimed is: 
     
       1. A process for preparing acetylene by the Sachsse-Bartholomé process by burning a natural gas/oxygen mixture in one or more burners to obtain a cracking gas which is cooled in two or more stages in burner columns, each burner having one or more burner columns assigned thereto, and said cracking gas being quenched with pyrolysis oil in the first cooling stage, to obtain a low boiler fraction comprising styrene, indene, benzene, toluene and xylenes from the one or more burner columns, which is cooled with direct cooling water and separated in a phase separator into an aqueous phase and an organic phase which consists of:
 8 to 18% by weight of styrene; 
 5 to 10% by weight of indene, 
 a total of 15 to 20% by weight of the sum of ortho-, para- and meta-xylene, 
 15 to 20% by weight of toluene and 
 8 to 10% by weight of benzene, 
 where the sum of all components adds up to 100% by weight; 
 
       and is introduced to the top of the one or more burner columns as a return stream, and recovering acetylene; 
       wherein the organic phase consisting of styrene, indene, benzene, toluene and xylenes from the phase separator is supplied to a selective hydrogenation over a catalyst which comprises at least one platinum group metal on an inorganic metal oxide as support, comprising 0.05 to 5% by weight of platinum group metal, based on the total weight of the catalyst, and wherein the selective hydrogenation is performed at a pressure in the range from 1 to 40 bar and a temperature in the range from 25 to 150° C. to selectively hydrogenate styrene, indene and derivatives thereof while preserving the aromatic rings, such that the selective hydrogenation of indene proceeds at a conversion of >96%. 
     
     
       2. The process according to  claim 1 , wherein the catalyst comprises palladium on aluminum oxide, titanium dioxide, zirconium oxide, silicon dioxide or mixtures thereof as a support. 
     
     
       3. The process according to  claim 1 , wherein the selective hydrogenation is performed in a fixed bed. 
     
     
       4. The process according to  claim 1 , wherein the selective hydrogenation is performed in a hydrogenation reactor which is started up with an inert liquid, especially benzene, toluene or a selectively hydrogenated benzene/toluene/xylene mixture, and to which the organic phase to be subjected to selective hydrogenation is gradually supplied. 
     
     
       5. The process according to  claim 1 , wherein the organic phase consisting of styrene, indene, benzene, toluene and xylenes from the phase separator, before being supplied to the selective hydrogenation, is depleted of residues of carbon monoxide present therein down to 5 ppm by weight, based on the total weight of the organic phase from the phase separator. 
     
     
       6. The process according to  claim 5 , wherein the depletion of carbon monoxide is effected by stripping with hydrogen. 
     
     
       7. The process according to  claim 5 , wherein the depletion of carbon monoxide is effected by distillation. 
     
     
       8. The process according to  claim 1 , characterized by thermal integration in the selective hydrogenation, by utilizing the heat of the product stream from the selective hydrogenation for preheating of the organic phase consisting of styrene, indene, benzene, toluene and xylenes and is to be subjected to the selective hydrogenation. 
     
     
       9. The process according to  claim 1 , wherein hydrogen is supplied to the hydrogenation reactor in such a way that an at least 10% excess, based on the sum of the chemical hydrogen consumption and the hydrogen dissolved in the hydrogenation reactor under the reaction conditions of the selective hydrogenation, is ensured. 
     
     
       10. The process according to  claim 5 , wherein the organic phase consisting of styrene, indene, benzene, toluene and xylenes from the phase separator, before being supplied to the selective hydrogenation, is depleted of residues of carbon monoxide present therein down to 1 ppm by weight, based on the total weight of the organic phase from the phase separator.